Endo 2-The Hypothalamo-adenohypophysial axis Flashcards Preview

LCRS > Endo 2-The Hypothalamo-adenohypophysial axis > Flashcards

Flashcards in Endo 2-The Hypothalamo-adenohypophysial axis Deck (23):
1

Describe the hypothalamus (4)

o Regulates the endocrine system
o Lies around the 3RD VENTRICLE in the brain
o Anterior: OPTIC CHIASMA lies at the front of the hypothalamus, and has an important role in sight
o Posterior: MAMMILLARY BODY at the back of the hypothalamus is important in the development of the nervous system

2

What the are the two lobes of the pituitary gland

o ANTERIOR LOBE (ADENOHYPOPHYSIS) - “grows up” and attaches to the base of the brain.
o POSTERIOR LOBE (NEUROHYPOPHYSIS) – nervous tissue “grows down” and attaches to the anterior lobe; consists mainly of nerve axons and nerve terminals

3

Describe the Link between the Hypothalamus and the Pituitary Gland

The region between the Hypothalamus and the pituitary gland is known as the REGION OF MEDIAN
EMINENCE
 Within the hypothalamus, HYPOTHALAMIC NUCLEI are present. These are clusters of nerve cell bodies.

4

What are the two types of nuerones in the HYPOTHALAMIC NUCLEI

There are two types of neurones within these clusters:
o Neurones that pass through the region of
median eminence and end at the
NEUROHYPOPHYSIS within the pituitary
gland
o Neurones that terminate at the region of
median eminence

5

How is blood supplied to the region of median eminence

SUPERIOR HYPOPHYSIAL ARTERY

6

What happens when the hypothalamic neurone is activated

HYPOTHALAMIC NEUROSECRETION occurs

7

Describe the process of HYPOTHALAMIC NEUROSECRETION

 NEUROSECRESTIONS (hypothalamic releasing/inhibiting hormones) are released within the
HYPOTHALAMO-HYPOPHYSIAL PORTAL SYSTEM
 Capillary collection of the neurosecretions in the Region of Median Eminence is fenestrated by the
PRIMARY CAPILLARY PLEXUS
 Circulation of the neurosecretions is within the LONG PORTAL VEINS and the SECONDARY CAPILLARY
PLEXUS
 The hypothalamic neurosecretion acts on the ANTERIOR PITUITARY TARGET CELLS, which release
ADENOHYPOPHYSIAL HORMONE into the CAVERNOUS SINUS, and then into the general circulation via the JUGULAR VEINS

8

What hormone is produced in Somatotrophes, what is the target cell

Somatotrophin
growth hormone
Protein
general body tissue, especially the liver

9

What hormone is produced in Lactotrophes what is the target cell

Prolactin
Proteins
breasts (lactating women)

10

What hormone is produced in Thyrotrophes what is the target cell

Thyrotrophin
(thyroid stimulating hormone; TSH)
Glycoproteins
thyroid

11

What hormone is produced in Gonadotrophes what is the target cell

Gonadotrophins
(Leutinizing hormone; LH
Follicle stimulating hormone; FSH)
Glycoproteins
testes (men), ovaries (women)

12

What hormone is produced in Corticotrophes what is the target cell

Corticotrophin
(adrenocorticotrophic hormone; ACTH)
Polypeptides
adrenal cortex

13

Which HYPOTHALAMIC HORMONES affect somatotrophin

o SOMATOTROPHIN RELEASING HORMONE (SRH/GHRH) stimulates release
o SOMATOSTATIN (SS) inhibits release

14

Which HYPOTHALAMIC HORMONES affect Prolactin

o DOPAMINE (DA) inhibits release (is also dominant hormone controlling prolactin release)
THYROTROPHIN RELEASING HORMONE (TRH)  stimulates release

15

Which HYPOTHALAMIC HORMONES affect Thyrotrophin

THYROTROPHIN RELEASING HORMONE (TRH)  stimulates release

16

Which HYPOTHALAMIC HORMONES affect Gonadotrophins (LH & FSH)

o GONADOTROPHIN RELEASING HORMONE (GnRH) simulates release

17

Which HYPOTHALAMIC HORMONES affect Corticotrophin (ACTH)

o CORTICOTROPHIN RELEASING HORMONE (CRH) stimulates release
o VASOPRESSIN (VP) stimulates release (secondary)

18

Describe the secretion and action on tissues of somatotrophin

 Secreted from the adenohypophysis (anterior pituitary lobe) and is transported to the body tissues and Liver
 Binding to receptors on general body tissues metabolic actions growth and development
 Binding to receptors on liver release of SOMATOMEDINS; mediators- IGF I and IGF II

19

5 Somatomedin metabolic actions:

o Stimulation of amino acid transport into cells e.g. muscles
o Stimulation of protein synthesis
o Increased cartilage growth
o Stimulation of lipid metabolism leading to increased fatty acid production
o Increased insulin resistance, leading to decreased glucose utilization and increased blood glucose
concentration

20

Describe control of somatotrophin production

Negative Feedback
 Somatotrophin and somatomedin release in itself inhibits further somatotrophin production via negative
feedback loops
 SOMATOSTATIN (SS) inhibits release



Positive feedback
SOMATOTROPHIN RELEASING HORMONE (SRH/GHRH) stimulates release


Other things that stimulate somatotrophin production include:
 Sleep stages III and IV
 Stress
 Oestrogens
 Exercise
 Fasting/hypoglycaemia
 Amino acids
 GHRELIN (from stomach)

21

Effects of prolactin

Main physiological effect:- BREAST LACTOGENESIS in post-partum women

 Other effects:
o Increased number of LH receptors in Gonads
o Renal Na+/Water reabsorption
o Steroidogenesis
o Immunological effects, e.g. stimulates T cells

 Effects during high circulating levels:
o Decreased LH release from the pituitary gland
o Decreased sexual behaviour – involves hypothalamus

22

Control of prolactin production

 Stimulus: suckling- stimulation of tactile receptors on breast nipple
 Inhibition of DA and stimulation of TRH via AFFERENT NEURAL PATHWAY
 OESTROGENS and IODOTHYRONINES also stimulate prolactin

23

How does prolactin stimulate milk production

via the ENDOCRINE EFFERENT NEURAL PATHWAY known as a NEUROENDOCRINE REFLEX ARC